The present inventor previously developed a process for purifying crude 1,2-bis(nicotinamido)propane by forming 1,2-bis(nicotinamido)propane oxalate and dissociating free 1,2-bis(nicotinamido)propane from the oxalate in an aqueous solution of potassium carbonate. The thus-formed free 1,2-bis(nicotinamido)propane is then crystallized, and recrystallized or purified with the use of silica gel column chromatography as disclosed in Japanese Patent Application Public Disclosure (Kokai) No. 56-75474.
However, this purification process through the oxalate salt of 1,2-bis(nicotinamido)propane as described above has a problem in that the oxalate salt is very difficult to be recrystallized, and, thus, the desired 1,2-bis(nicotinamido)propane can only be obtained with a low purity, since free 1,2-bis(nicotinamido)propane is obtained from a mixture containing various impurities such as nicotinic acid, N-(2-ethoxycarbonylamino)propylnicotinamide, N-(2-ethoxycarbonylamino-1-methyl)ethyl-nicotinamide, etc. The desired product thus obtained generally contains such impurities at a proportion of about 0.4 to 1.0% (ratio of area) as determined in the high performance liquid chromatography (HPLC). Further, it is very difficult to completely remove the impurities by recrystallization of 1,2-bis(nicotinamido)propane, and the recrystallized product generally contains such impurities at a proportion of about 0.1 to 0.3 (ratio of area) as determined by HPLC. It is therefore necessary to subject the product to further purification by silica gel chromatography, but such a purification procedure is disadvantageous from the standpoint of production cost and operation in the production of a large quantity of 1,2-bis(nicotinamido)propane.
As a result of extensive studies on an efficient purification process of 1,2-bis(nicotinamido)propane, the present inventor found that the above compound can be purified effectively according to the process of the present invention hereinafter described in detail, and completed the present invention.